Exercise treadmills are widely used for various purposes. Exercise treadmills are, for example, used for performing walking or running aerobic-type exercise while the user remains in a relatively stationary position, further, exercise treadmills are used for diagnostic and therapeutic purposes. For all of these purposes, the person on the exercise treadmill normally performs an exercise routine at a relatively steady and continuous level of physical activity. Examples of such treadmills are illustrated in U.S. Pat. Nos. 4,635,928, 4,659,074, 4,664,371, 4,334,676, 4,635,927, 4,643,418, 4,749,181, 4,614,337, 6,095,951 and 6,572,512.
Exercise treadmills typically have an endless running surface which is extended between and movable around two substantially parallel pulleys at each end of the treadmill. The running surface usually includes a belt made of a flexible material extended around the pulleys. The belt is normally driven by a motor rotating the front pulley. The speed of the motor is adjustable by the user through a set of user controls so that the level of exercise can be adjusted to simulate running or walking as desired.
The belt is typically supported by a deck or support surface beneath the upper surface of the belt. The deck is usually composed of wood or MDF, in order to provide the required support. In addition, a low-friction sheet or laminate is usually provided on the upper deck surface to reduce the friction between the deck and the belt. In most cases, decks are relatively rigid which can result in high impact loads on the user's feet, ankles and knees as the user's feet contact the belt and the deck. This is often perceived by users as being uncomfortable and further can result in unnecessary damage to joints as compared to running on a softer surface.
Because the typical treadmill has a very stiff, hard running surface and can become uncomfortable for extended periods of running, manufacturers have sought to make the running surface more resilient in an attempt to improve user comfort. U.S. Pat. Nos. 3,408,067, 4,350,336, 4,616,822, 4,844,449, 5,279,528, 5,441,468, 5,454,772 and 6,095,951 disclose examples of resilient deck support on treadmills to reduce impact loads. While reducing impact loads, these approaches have certain disadvantages. In some cases due to long usage, the resilient material loses its resiliency over time and becomes less resilient. In other cases, where the resiliency or spring rate of the deck supports made of a resilient material is constant, the supports usually will not provide adequate support and comfort for users having different weights and running styles. Another approach using resilient supports having a variable spring rate, such a shown in U.S. Pat. No. 6,095,951 do not allow the user to adjust the deck to achieve an individual comfort level. By the same token where the location of resilient support members can be changed, as described in U.S. Pat. No. 4,350,336, the resiliency of the deck is uneven along its longitudinal surface.